2-sided plane: bottom image flipped?
Three possibilities (at least) :

Modifying the scale in the texture panel

Setting the texture (of color2) X scale to -1 will flip the image horizontally.



Adding a vector mapping node

The same principle, but set up in the material nodes :



Adding a second UV map


Create a second UV map in the properties panel using the '+' button (1) and eventually rename it
Unwrap in that new UV map and scale it -1 along X using S+X+-1 (in 2)
Add UV map nodes in the material (3)